Titanium alkoxides and chelates of titanium alkoxides are well known and have broad industrial application. But the chemistry of these compounds is complex and often is not well understood. In some instances this has limited the use of titanium in an application, and catalysis of ester manufacture is one of those instances. This invention is concerned with advancing the chemical technology of titanium chelates and esterification catalysis.
Since 1950 the catalyst characteristics of titanium compounds, as well as those of tin, antimony and other organometallics were widely investigated as demonstrated by U.S. Pat. No. 3,254,959. While the earliest focus of such work was on organometallic catalysis of high temperature polyesterifications (see British Specification No. 1,246,346), the use of tetraisopropyl titanate catalysis in manufacture of plasticizer esters became commercially important soon after its disclosure in the Werber patents, U.S. Pat. Nos. 3,056,817 and 3,056,818. These patents demonstrate the utility of titanium alkoxides at temperatures above 200.degree. C. and cite important advantages in less degrading of alcohols and refining to high purity esters without caustic wash. Similar disclosures for titanic acid appear in U.S. Pat. No. 2,727,881 and in British Pat. No. 1,058.242 and a variety of titanium and tin compounds have been disclosed in U.S. Pat. Nos. 3,254,959; 4,020,010; 4,260,735; and in British Pat. No. 1,246,346 with potential advantages of faster reactions and the avoiding of undesirable side effects in both general purpose and polymeric esters.
Disadvantages associated with titanium catalysis are well known and are the subject of several patents. The largest disadvantage of titanium is the high temperature range of 200.degree.-220.degree. C. required for practical reaction rates. Synthesis of organometallic catalysts with increased activity has been the object of many investigations. Combinations of titanates and tin salts are proposed by Vogt in U.S. Pat. No. 4,020,010 as more active than the individual components. A number of workers have disclosed methods to avoid the increase in acidity during steam distillation and the disadvantages of washing in refining processes. Treatment with solid bases to avoid these problems is described by Chilton in U.S. Pat. No. 3,818,071, Ghanayem in U.S. Pat. No. 4,007,218 and Sagara in U.S. Pat. No. 4,284,793, while an intricate heat treatment and filtration process is described in a recent U.S. Pat. No. 4,216,337 by Baba. In U.S. Pat. Nos. 4,506,091 and 4,526,725 that are related to the instant invention, there is disclosed the use of chelating agents to assist in the removal of titanium residues from the reaction mixture, and to make alkoxy titanium chelates that show higher catalytic activity and are more easily removed from the ester in the refining process. Fully chelated titanium compounds are well known and are valuable commercial compounds, reference for which may be found in Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 23 3rd Ed. 1983, John Wiley & Sons, New York, N.Y. and Field & Case, The Organic Chemistry of Titanium, 1965, Butterworths. The use of titanium triethanolamine chelate (Tyzor TE) is known and exhibits a lower order of activity in comparison with alkoxy titanates. As disclosed in U.S. Pat. No. 4,260,735, the use of TE is reported to have advantange in retarding formation of ether by-products in catalysis of certain polymeric esters.
From a commercial view the use of titanium compounds in ester catalysis has been limited to the alkoxy titanates TPT and TBT for the most part. Notable exceptions are the applications of TE, mentioned above, and the very recent introduction and use of Tyzor GR, an alkoxy titanium chelate based on the disclosure in U.S. Pat. No. 4,526,725.
This invention discloses new titanium chelate compositions that provide both improved catalysts for ester manufacture and advantage of insight to the nature and fate of the catalyst.
Compositions of the invention include chelates that are derived from tetra-alkyl titanates and dialkanolamines as well as certain hydrolysis products of the chelates so derived.
In Deardorff U.S. Pat. No. 4,506,091, there is described the use of chelating agents for the treatment of titanium catalyzed reaction mixtures, the agents being added prior to steam distillation and assisting in making the hydrolysis and precipitation of catalyst residues efficient and without increase of acid value; giving high purity esters in only a further filtration step, and avoiding the caustic and water wash usually required to get equivalent results.
In Deardorf patent, U.S. Pat. No. 4,526,725, there is described the use of chelating agents to make alkoxy titanium chelate (ATC) compositions that are improved catalysts for ester manufacture. These compositions, which include alkyl groups with more than three carbon atoms to lower water sensitivity, provide advantages in refining as well as a surprising enhancement in catalytic activity.
By these disclosures there is provided compositions and methods that are highly effective to avoid certain problems that are common to ester manufacture. But it is evident that further improvements in reaction rate and process design might be made if one had better insight of the process chemistry. This invention is concerned with the discovery of new information related to the structure and the fate of catalyst species, and of new titanium chelate compounds.